This section is intended to provide a background or context to the invention disclosed below. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise explicitly indicated herein, what is described in this section is not prior art to the description in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
ACKacknowledgement (e.g., positive acknowledgement)CoMPcoordinated multi-pointCRCcyclic redundancy checkDLdownlink (from the base station to the UE)eNode B (eNB)evolved Node B (LTE base station)E-UTRANevolved UTRANFFTfast Fourier transformGWgatewayHARQhybrid automatic repeat requestICinterference cancellationLMMSElinear minimum mean squared error (MMSE)LTElong term evolutionMIMOmultiple-input, multiple-outputMMSEminimum mean squared errorMU-MIMOmulti-user MIMONACKnegative acknowledgementNCEnetwork control elementNDInew data indicatorPDCCHphysical downlink control channelPDSCH physical downlink shared channelSINRsignal to interference plus noise ratioTTItransmission time intervalUEuser equipmentULuplink (from UE to base station)UMTSuniversal mobile telecommunications systemUTRANuniversal terrestrial radio access network
Non-linear receivers are known to improve the spectral efficiency in UL multiuser-MIMO (MU-MIMO) and UL coordinated multipoint systems (CoMP). A good example for CoMP is a large stadium with a number of eNBs coordinated between each other to support a need for higher data rates during a sporting event.
The non-linear receivers achieve significant capacity improvements and comprise two stages. The first stage is a front-end linear receiver and this stage is followed by a second stage receiver that performs interference reconstruction, interference cancellation and linear reception.
In non-linear receivers, interference reconstruction is achieved after receiving hard or soft bits from other eNB receivers. That is, the eNB receivers exchange hard or soft bits with other eNB receivers and use hard or soft bits in, e.g., the interference reconstruction and cancellation.
Non-linear receivers suffer from latency issues and therefore delay HARQ signaling to the UEs. For instance, the receiver processing cannot be completed within a TTI with a nonlinear receiver. The eNB is required to complete the two stage receiver processing in one TTI and report ACK or NACK information to a UE. However, the second stage is required to wait for exchange of decoded packets, interferer reconstruction, interference cancellation and other receiver processing and hence adds to latency.
Signaling HARQ information to the UE based only on the first stage of a non-linear receiver may result in inefficient use of the UL resource. As an example, assume that the first stage result is a decode failure and hence a NACK is sent to the UE. However, completion of the second stage of the receiver (e.g., interference cancellation receiver) results in a decode success and hence the resource for retransmissions from the UE is wasted, thereby leading to inefficient use of the UL resource.